Antidepressants increase adult hippocampal neurogenesis in animal models, but the underlying molecular mechanisms are unknown. In this study, we used human hippocampal progenitor cells to investigate the molecular pathways involved in the antidepressant-induced modulation of neurogenesis. Because our previous studies have shown that antidepressants regulate glucocorticoid receptor (GR) function, we specifically tested whether the GR may be involved in the effects of these drugs on neurogenesis. We found that treatment (for 3-10 days) with the antidepressant, sertraline, increased neuronal differentiation via a GR-dependent mechanism. Specifically, sertraline increased both immature, doublecortin (Dcx)-positive neuroblasts (+16%) and mature, microtubulin-associated protein-2 (MAP2)-positive neurons (+26%). This effect was abolished by the GR-antagonist, RU486. Interestingly, progenitor cell proliferation, as investigated by 5'-bromodeoxyuridine (BrdU) incorporation, was only increased when cells were co-treated with sertraline and the GR-agonist, dexamethasone, (+14%) an effect which was also abolished by RU486. Furthermore, the phosphodiesterase type 4 (PDE4)-inhibitor, rolipram, enhanced the effects of sertraline, whereas the protein kinase A (PKA)-inhibitor, H89, suppressed the effects of sertraline. Indeed, sertraline increased GR transactivation, modified GR phosphorylation and increased expression of the GR-regulated cyclin-dependent kinase-2 (CDK2) inhibitors, p27(Kip1) and p57(Kip2). In conclusion, our data suggest that the antidepressant, sertraline, increases human hippocampal neurogenesis via a GR-dependent mechanism that requires PKA signaling, GR phosphorylation and activation of a specific set of genes. Our data point toward an important role for the GR in the antidepressant-induced modulation of neurogenesis in humans.
Psychoimmunology is a rapidly maturing area of scientific endeavor that provides a compelling integrative link between the immune system and its response to stress and psychiatric illness. Stress initiates pathological changes by activating the immune and endocrine systems. Inflammation is at the core of the complex and interactive systems that both contribute to and result from psychopathology. Consequently, inflammation research advances our knowledge of the pathology of depression, schizophrenia, chronic fatigue syndrome, posttraumatic stress disorder and a host of co-morbid conditions, notably diabetes, cardiovascular disease and cerebrovascular disease. The possible mechanisms underlying the bidirectionality of co-morbid medical and psychiatric disorders can be viewed as a consequence of inflammatory changes. These emerging novel concepts illustrate how the knowledge of inflammation can enable meaningful integration of psychopathology with physical co-morbidity. The innovative articles in this volume highlight the intricate link between psychiatry and psychoimmunology and underscore the central role of inflammation in furthering our understanding of the pathophysiology underlying mental health and illness.
The septotemporal axis of the hippocampus separates it into domains with unique molecular, cellular, downstream connectivity and behavioral profiles, and yet very little is known about the ontogenesis of these highly specialized subcircuits. Here, we used viral tracing, optogenetic-assisted patch clamping, chemogenetics and behavior in mice to examine changes in domain-defined hippocampus efferent projections from postnatal day (P)10 to P60. We found distinct anatomical and synaptic developmental signatures in ventral and intermediate CA1 downstream connectivity, with unique contributions to the prelimbic and infralimbic subregions of the medial prefrontal cortex (mPFC). Inhibition of the ventral CA1 (vCA1)-mPFC pathway during juvenility led to a deficit in adult cognitive flexibility exclusively in females, establishing a sex- and pathway-specific sensitive period preceding the stabilization of vCA1-mPFC synaptic transmission. Our data elucidate domain- and target-defined postnatal maturation of hippocampus efferents, identifying a sex-specific sensitive period with crucial implications for early life influences on adult cognition.
Abstract Depression and anxiety are major global health burdens. Although SSRIs targeting the serotonergic system are prescribed over 200 million times annually, they have variable therapeutic efficacy and side effects, and mechanisms of action remain incompletely understood. Here, we comprehensively characterise the molecular landscape of gene regulatory changes associated with fluoxetine, a widely-used SSRI. We performed multimodal analysis of SSRI response in 27 mammalian brain regions using 310 bulk RNA-seq and H3K27ac ChIP-seq datasets, followed by in-depth characterisation of two hippocampal regions using single-cell RNA-seq (20 datasets). Remarkably, fluoxetine induced profound region-specific shifts in gene expression and chromatin state, including in the nucleus accumbens shell, locus coeruleus and septal areas, as well as in more well-studied regions such as the raphe and hippocampal dentate gyrus. Expression changes were strongly enriched at GWAS loci for depression and antidepressant drug response, stressing the relevance to human phenotypes. We observed differential expression at dozens of signalling receptors and pathways, many of which are previously unknown. Single-cell analysis revealed stark differences in fluoxetine response between the dorsal and ventral hippocampal dentate gyri, particularly in oligodendrocytes, mossy cells and inhibitory neurons. Across diverse brain regions, integrative omics analysis consistently suggested increased energy metabolism via oxidative phosphorylation and mitochondrial changes, which we corroborated in vitro; this may thus constitute a shared mechanism of action of fluoxetine. Similarly, we observed pervasive chromatin remodelling signatures across the brain. Our study reveals unexpected regional and cell type-specific heterogeneity in SSRI action, highlights under-studied brain regions that may play a major role in antidepressant response, and provides a rich resource of candidate cell types, genes, gene regulatory elements and pathways for mechanistic analysis and identifying new therapeutic targets for depression and anxiety.
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